I solved the problem.....
Turns out this was NOT a graphic problem !!!
I have 2 gameports: 1 standard and 1 on my soundcard.
On 1 port my sidewinder force feedback joystick was plugged in, on the other my GAMEBIRD.
It seems FMS doesn't like that.
I removed my sidewinder from the gamecontrols in WinXP and now FMS runs fine (75fps@1024x768)
At last!!!
Greetz Gaaaz :p